1. Field of the Invention
The present invention relates to cables and, particularly, to a coaxial cable.
2. Discussion of Related Art
A coaxial cable is an electrical cable including an inner conductor, an insulating layer, and a conducting layer, usually surrounded by a sheath. The inner conductor can be, e.g., a solid or braided wire, and the conducting layer can, for example, be a wound foil, a woven tape, or a braid. The coaxial cable requires an internal insulating layer (i.e., a dielectric) to act as a physical support and to maintain a constant spacing between the inner conductor and the conducting layer, in addition to electrically isolating the two.
The coaxial cable may be rigid or flexible. Typically, the rigid type has a solid inner conductor, while the flexible type has a braided inner conductor. The conductors for both types are usually made of thin copper wires. The insulating layer, also called the dielectric, has a significant effect on the cable's properties, such as its characteristic impedance and its attenuation. The dielectric may be solid or perforated with air spaces. The shielding layer is configured for ensuring that a signal to be transmitted stays inside the cable and that all other signals to stay out (i.e., acts as a two-way signal shield). The shielding layer also serves as a secondary conductor or ground wire.
The coaxial cable is generally applied as a high-frequency transmission line to carry a high frequency or broadband signal. Sometimes, DC power (called a bias) is added to the signal to supply the equipment at the other end, as in direct broadcast satellite receivers, with operating power. The electromagnetic field carrying the signal exists (ideally) only in the space between the inner conductor and conducting layer, so the coaxial cable cannot interfere with and/or suffer interference from external electromagnetic fields.
However, the conventional coaxial cable is low in yield and high in cost. Therefore, a coaxial cable that has great shield effectiveness and that is suitable for low-cost mass production is desired.